UHC or Broadband

[Kenza]

Hi! What would be a better filter to use under urban skies: The astronomik CLS CCD or the UHC filter? Or should I get both of them?

Also, I have a 5" apo. At woodland hills telescope it says that the astronomik UHC Economy filter is better for scopes up to 5 " while the standard UHC is better for larger scopes. Does anybody why that is?

And finally, will the OIII filter be of any use to me since I have a smaller scope, since I read somewhere that these filters are for larger scopes.

[rwilkey]

The UHC filter would be the best visual filter for your telescope, the CLS CCD is for DSLR cameras and not inteneded for visual use, so go careful on this point, make sure any filter you buy is for visual use before you purchase, if this is what you intend. The OIII filter will also work well in your aperture, yes, they work better on bigger apertures but not exclusively so. My advice is to get the UHC filter first and see how you get on. All nebula filters work better in dark sky locations although they are also good at blocking out light pollution as well. The UHC is the most broadband of them all. The Oiii is really a line filter, operating at a very narrow bandwidth, hence the standard recommendation for using them in larger apertures, but don't be afraid to use them, for what they are intended (diffuse nebula) they can be very beneficial. I use the UHC and the OIII in my 4" refractor quite successfully.

[John]

The UHC filter (which is in the narrowband category) will be more effective than a broadband.

I too use an O-III in scopes down to 4" in aperture and it works well. My O-III filter is an Astronomik which have a little more generous band pass width than most O-III filters. The Baader O-III is a good quality filter but is not so suitable for smaller scopes as it has a very narrow band pass width.

[Kenza]

Well, I plan to do DSLR photography, so I should then also get the CLS CCD filter. Ok, I'll first get the UHC and OIII and then the CLS. Thanks!

[Scooot]

I'm also in the market for a filter, and as well as reading all the helpful threads on here I also found these two links very helpful:

http://www.lumicon.com/pdf/3filterspec_prnt.pdf

http://www.knoxvilleobservers.org/dsonline/tips/lprfilters.html

I was favouring the lumicon deepsky filter at first until I read the second link and I am now firmly in the uhc camp as suggested before me. I found lumicon s PDF very helpful though as it explained the various band widths and which light bands affected the various objects.

[John]

Interesting stuff. There is no de facto standard for the specification of a UHC or an O-III filter. The different brands have different characteristics depending mostly on their band pass width. The trick is to work out which one suits you, your scope and your wallet !

I just use one at the moment - an Astronomik O-III in the 2" fitting. It's a great filter and very versatile

[Scooot]

Interesting stuff. There is no de facto standard for the specification of a UHC or an O-III filter. The different brands have different characteristics depending mostly on their band pass width. The trick is to work out which one suits you, your scope and your wallet !

I just use one at the moment - an Astronomik O-III in the 2" fitting. It's a great filter and very versatile

yes, I think I have a better idea of what to look for now and how to compare. I was considering an Oiii but I think a uhc would be more versatile for me at the moment, In terms of brand I haven't really decided, and I am also considering an astronomic, also read some good things about castell. The lumicon was in my mind as they're on sale at the moment, 120us instead of 168 (plus vat and carriage), still quite dear, but as I have tv eyepieces, it'd be a bit silly not to get something good.

thanks for your advice

[John]

yes, I think I have a better idea of what to look for now and how to compare. I was considering an Oiii but I think a uhc would be more versatile for me at the moment, In terms of brand I haven't really decided, and I am also considering an astronomic, also read some good things about castell. The lumicon was in my mind as they're on sale at the moment, 120us instead of 168 (plus vat and carriage), still quite dear, but as I have tv eyepieces, it'd be a bit silly not to get something good.

thanks for your advice

I use Tele Vue and Pentax eyepieces as well. I found the Astronomik filter give better renditions of stars than other filters I've used which is what swayed me to invest in it. I agree that a UHC is a bit more versatile overall than an O-III but for the objects I'm interested in I find the O-III enhances the contrast a little more.

For a first filter a UHC makes sense though and even the lower cost ones can make a real difference to the views of nebulae, some objects stunningly so.

[Spec-Chum]

I can't even see the veil without my UHC, pop it in the chain and bang, there it is!

Wonderful sight too, worth it for the price of a filter alone...

[John]

I can't even see the veil without my UHC, pop it in the chain and bang, there it is!

Wonderful sight too, worth it for the price of a filter alone...

Totally agree

[StarSteve]

One can learn a great deal from looking at the actual filter diagrams, without being an expert (which I am not).

From the start UHC was just a product name used (still used) by Lumicon, as I understand it. The filter is popular so the term "UHC" has since been copied/stolen/borrowed by other manufacturers, which has the effect that UHC means nothing apart from being contrast enhancing one way or another. This is evident if looking at specs, compare for example Baaders idea of UHC to Lumicon and it's a very different thing.

With OIII I believe it's basically a matter of how narrowly the filter focus on the 501nm oxygen line. More narrow means more effect on the nebulae that emits lots of OIII and less when pointed at something else. Some "OIII" filters seem to have a rather broad reach presumably to make them less specialized and "more useful" in general, which to me seems like a contradiction. If you want a filter for general use why would you get a narrowband one like OIII or H-Beta in the first place?

Here is a very interesting comparison at CN of how different Lumicon filters behaved at different DSO. Note the above though, the values means little unless you have actual Lumicon filters of the corresponding types.

Steve

[StarSteve]

Here is an example of what I was talking about, look at the diagrams for Lumicon UHC and Baader UHC. Totally different beasts that must render totally different results.

[michael.h.f.wilkinson]

Not totally different, but certainly not the same. BTW, a filter for visual can be used for imaging, and vice-versa (with the exception of H-alpha, which the human visual system cannot easily at night (rods aren't sensitive in that area). It is more a matter of being optimal for a particular use. Broad-band imaging filters take issues like colour balance into account, a visual filter need not (them rods in your retina, again). Narrowband filters for visual tend to have broader pass bands, to allow more light through, at the expense of more background. Photographic ones have narrow pass bands, as they can deal with lower light conditions through extending exposure times.

[michael.h.f.wilkinson]

One point I forgot to mention is that visual filters need not block IR, photographical filters do. You can of course add an IR block filter into the optical pathway for imaging with a visual filter.

[StarSteve]

One point I forgot to mention is that visual filters need not block IR, photographical filters do. You can of course add an IR block filter into the optical pathway for imaging with a visual filter.

Hm, I know very little about AP, but don't the astrophotography crowd remove IR cut filters from cameras all the time? That seems contradictory to having filters that block IR? I must be missing something.

Steve

[michael.h.f.wilkinson]

Hm, I know very little about AP, but don't the astrophotography crowd remove IR cut filters from cameras all the time? That seems contradictory to having filters that block IR? I must be missing something.

Steve

They remove the IR block filter because it also cuts the H-alpha sensitivity. IR itself is often unwanted when using refractors, which are generally not corrected properly for IR wavelengths. Reflectors do not have these problems. What you want is a filter that lets all visible light through, but not IR. Alternatively, you can use a near-IR pass filter, and image only the near IR (refocusing may be needed in refractors).

[John]

..... Some "OIII" filters seem to have a rather broad reach presumably to make them less specialized and "more useful" in general, which to me seems like a contradiction. If you want a filter for general use why would you get a narrowband one like OIII or H-Beta in the first place?.....

My Astronomik O-III is one of the broader reach O-III's and I find it extremely effective in my scopes from 4" aperture to 10". I've tried a number of other O-III and UHC filters and the Astronomik is the best (and most expensive ) that I've used.

[StarSteve]

They remove the IR block filter because it also cuts the H-alpha sensitivity. IR itself is often unwanted when using refractors, which are generally not corrected properly for IR wavelengths. Reflectors do not have these problems. What you want is a filter that lets all visible light through, but not IR. Alternatively, you can use a near-IR pass filter, and image only the near IR (refocusing may be needed in refractors).

I see. So the camera filters are a bit generous with what they cut and essentially they are replaced with a filter that only does what it's supposed to. Ok, that makes sense, thanks.

Steve

[StarSteve]

My Astronomik O-III is one of the broader reach O-III's and I find it extremely effective in my scopes from 4" aperture to 10". I've tried a number of other O-III and UHC filters and the Astronomik is the best (and most expensive ) that I've used.

Hm.. Astronomik doesn't look that broad reach to me though. Looks identical to the Baader, goes slightly higher than the Orion and a little bit more broadband than the Lumicon. Unless I am misreading the diagrams. The Denkmeier is broader though, including above 650nm and below 410nm or so.

Steve

[John]

Hm.. Astronomik doesn't look that broad reach to me though. Looks identical to the Baader, goes slightly higher than the Orion and a little bit more broadband than the Lumicon. Unless I am misreading the diagrams. The Denkmeier is broader though, including above 650nm and below 410nm or so.

Steve

I've compared my Astronomik O-III to the Baader O-III and there is a noticeable difference in band pass width making the Astronomik much more satisfying to use in smaller scopes, to me at least.